Object

An object is an instance of a class stored in a set of memory locations.

Related concepts:  ClassTypeValue

Closest Wikipedia entry:  Object-oriented programming — Object-oriented programming (OOP) is a programming paradigm based on the concept of objects, which can contain data and code: data in the form of fields (often known as attributes or properties), and code in the form of procedures (often known as methods). In OOP, computer programs are designed by making them out of objects that interact with one another. Many of the most widely used programming languages (such as C++, Java, and Python) are multi-paradigm and support object-oriented programming to a greater or lesser degree, typically in combination with imperative programming, procedural programming and functional programming.

Misconceptions about Object

35 documented Misconceptions

AccessingInexistentPropertyError — JavaScript

Accessing a non existent property on an object produces an error

AssignmentCopiesObject — Java

Assignment copies the object

AssignmentCopiesObject — JavaScript

Assignment copies the object

AssignmentCopiesObject — Python

Assignment copies the object

BoxedNull — Java

Passing null to a wrapper class constructor creates an object representing the absence of a value

ChainedMethodsNotCalledFromOutside — Java

Chained methods are all called on the object at the beginning of the chain

EqualityOperatorComparesListIdentities — Scratch

(list a) = (list b) compares the identities of list a and list b

EqualityOperatorComparesObjectsValues — Java

o==p compares the objects referred to by variables o and p

EqualityOperatorComparesObjectsValues — JavaScript

The equality operator compares two objects' values

EqualsComparesReferences — Java

o.equals(p) compares the references stored in the variables o and p

FrameIsClassInstance — Java

A stack frame is the same as an instance of a class

IdentifierAsStringInBracketNotation — JavaScript

An identifier used to access a property with the bracket notation is treated as a string

MethodAsField — Java

Each object contains its own special fields for all of its methods

MultiReferenceVariable — Java

A reference variable can point to multiple objects

NestedObjectsImplyNestedClasses — Java

If objects are part of a containment hierarchy, their classes are nested, too

NoBracketNotationForObjects — JavaScript

Square brackets cannot be used to access properties of an object

NoFieldInheritance — Java

An object contains only the fields declared in its class

NoFieldlessObjects — Java

Objects without instance variables can't exist

NoGlobalObject — JavaScript

There isn't a global object

NoInsideMethodCallInConstructor — Java

It is foirbidden to call other methods on the same object while inside its constructor

NullIsObject — Java

null is an object

NullIsObject — JavaScript

null is an object

ObjectAsParameterIsCopied — JavaScript

Objects are passed by value

ObjectLabeledWithConstructorSignature — Java

In stack and heap diagrams, an object on the heap is labeled like a stack frame of a constructor call

ObjectLabeledWithVariableName — Java

In stack and heap diagrams, an object on the heap is labeled with the name of the variable that refers to it

ObjectsMustBeNamed — Python

A variable is needed to instantiate an object

PrimitiveIsObject — Java

Primitive values are heap objects

ReferenceLabeledWithDynamicType — Java

In stack and heap diagrams, reference variables are labeled with the types of the objects they refer to

SuperclassObjectAllocated — Java

When instantiating an object of a subclass, an object of a superclass is also allocated

ThisAsField — Java

this is a special field in the object

ThisAssignable — Java

One can assign to this

ThisAssignable — JavaScript

One can assign to this

ThisExistsInStaticMethod — Java

this is a local variable, also in static methods

VariablesHoldObjects — Java

A variable of a reference type contains a whole object

VariablesHoldObjects — Python

A variable contains a whole object